The chemistry of antifoul paint?

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jfm

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Can anyone explain the chemistry of antifoul paint please?

My boat is about to start its 5th season so has 8 layers of a/f already on it, and if I do "the usual" in next couple of months it will have 10 coats. (2 each time). Ok, it is soft antifoul so some has eroded away in 8000nm of running, but not much. You can still feel a "step" if you run your finger from the unpainted topsides onto the paint.

Why do we do this? If I have a thick layer of a/f paint already on the hull why should I apply more? Cant I just just jetwash the slime off the hull and crane it back in, with no new paint? It is already fully painted in antifoul paint, so why add more? Or does the paint lose its poisonous properties after a year, in which case it is now just inert paint without any antifoul/poison properties left in it?

If it has gone a bit inert, why should I put 2 coats on now? surely one is fine? If you do 2 coats, exactly what purpose does the first coat serve? Is it there to give enough thickness when the paint erodes as the boat moves? If so, I'll use just one coat becuase my paint isn't eroding that fast (maybe I need to drive faster??). Or is it there becuase it adds more of the poisonous chemical (in which case, does the poisonous part of the first coat move osmotically thru to the surface of second coat, which is where the weed grows? Or what?

I'm really tempted just to crane her out, jetwash, clean sterngear, and crane back in.

Can anyone explain the chemistry? Thanks
 
As far as I understand the noxious stuff is held in a pretty non reactive matrix of the rest of the paint and slowly leaches out thus keeping the slime/weed/barnacles at bay.

With 'hard' antifouling what is left at the end of the season is , in theory, just the non reactive 'carrier' matrix, hence the need to recoat.

the instructions for 2 coats, are, i presume are to give sufficient film thickness to generate enough noxious stuff in the coating. I see no reason why 1 thick coat should not work as well.

With 'soft/eroding' a/foul such as used by our raggie bretheren, the matrix erodes to reveal fresh anti-weed rather than it being leached out.

Thats as i understand it, but open to correction
 
I use an eroding antifoul International Optima, works exceptionally well. overcoats most traditional antifouls and at the end of the season only a fraction left say out of two coats a half a coat thickness .

Rather than a 16th of an inch each year build up.
 
On the International web site they are quite specific (you could say that they would be anyway) that all the paint designated for the underwater area is used even if extra coats are needed. Like others I assume that the thickness is necessary for the leaching to last the requisite time i.e. one season.

From their web site:

Hints
Mixing Stir well before use.
Thinner YTA085 Thinners No.3
Thinning Thinning is not recommended.
Cleaner YTA085 Thinners No.3
Other True colour will develop after immersion. Take care to apply all the paint calculated even if it means applying an extra coat. It is important for performance to apply the correct thickness.


Some Important Points
To prevent premature failure, ensure the correct amount of paint is applied using the coverage as a guide. Product temperature should be minimum -5°C and maximum 35°C. Ambient temperature should be minimum -5°C and maximum 35°C. Substrate temperature should be minimum 1°C above dew point and maximum 35°C.


I am curious as to how long you wait before removing the existing coats. 5 years ?

Tom
 
Thnaks guys for those replies. That means I have a very thick layer of dead/inert matrix with no poison in it. Damn! You know what, I'm tempted to experiment. Even if you apply new paint it doesn't work that well. So I might just crane her out and jetwash, and see how fast the weed grows. If the paint is dead, the weed will grow fast, in which case I can crane her out again and paint it (with Bandit's optima). But it might work fine, in which case I avoid the paint thickness build-up. I've nowt to lose, except the cost of a crane out and jetwash in the slings
 
Think you'll be wasting your time jfm. Have tried the same except I've scrubbed whilst in water and the weed re-appeared very quickly. Now using the tcm potion of trilux and copper powder and am hoping to get at least 2 years without painting again. I will report back as time progresses.
 
FWIW last year I used Interspeed Ultra in Dover and it worked a dream. Never had more than a coating of slime even at the end of the year lift out.

More than could be said for the outdrive - this year trying the lanolin coating on that.

Tom
 
I researched this in some detail for a story in MBY last year. Even with a soft anti-fouling you get left with an inert matrix of paint once the copper oxide has leached out of the surface layer. Some of this will erode with tide/movement of boat through water (and you can assist it by gentle brushing) but if your boat is static in a marina for even a couple of weeks, slime can grow on the dead matrix providing an even more inert layer for barnacles and weed to grow on.

Almost any fresh antifouling paint starts off being very effective but at some point it reaches a point where either all the copper has leached out or the inert matrix is so thick that the active ingredients can't reach the surface in sufficient quantity to be effective.

In theory the exception to this rule is a true self-polishing copolymer. Like the old TBT based paints these don't rely on the friction of water passing over the hull to remove the dead matrix but react with static water gradually dissolving to reveal fresh paint regardless of whether the boat is moving. Hence in theory you can paint on as many layers you like and it will remain as effective as the day you painted it right up until the final layer wears through.

International have recently launched one of these called Micron 66 into the superyacht market and will soon be available for leisure craft in the UK. I was allowed a trial sample to use on my boat last season which has proved very effective, although it appears to have worn right through in some areas.

The one thing I would say is that careful application of the right kind of paint is likely to make a much bigger difference to its efficiency than choosing one well known brand over another. In other words prepare the surface well, mix the paint properly, apply it at the recommended coverage rates, definitely do two coats and once in the water try to keep slime off with the occasional blast or scrub. The best tip I have ever had for a motorboat is to apply one layer of hard antifouling followed by one of soft. The soft is slightly more potent but if it does wear off completely there's a hard layer waiting underneath to kick into action.
 
Thanks for that Hugo and others, very interesting. I'm going to try that micron 66 stuff then. I'll be buying it from the big Antibes superyacht paint suppliers anyway, so shouldn't have any problem getting it if it is already available to the superyacht market (unless I have to buy a 50gallon drum...!). I'll ask at the paint shop tomorrow and report back if there is anything interesting re price/availbility

You said it wore right through in same areas. I'd love it if that happened. What I hate about hard matrix antifouls is that they WONT rub off!
 
What works where seems very localised Noni, maybe based on the particular type of slime/weed you have, and the water temp perhaps. I had Interspeed Ultra the time before last, in the Med (Antibes), in black colour, and it wasn't very good! I'm still carrying around 30 kilos of it in the form of two coats of dead matrix!
 
[ QUOTE ]
The best tip I have ever had for a motorboat is to apply one layer of hard antifouling followed by one of soft. The soft is slightly more potent but if it does wear off completely there's a hard layer waiting underneath to kick into action.

[/ QUOTE ]

This is an excellent idea and I believe one option is for jmf to apply one coat of soft on top of the 70% depleted hard.

My boat has old copper coat which isnt really adequate on its own so a coat of soft is added, once the soft goes the copper coat is there to give a placebo protection.

When doing this you need to double up coats to first 3 ft of bow and sides that scrub.

Unfortunately for jfm this will only work for one year and then next year there is a real problem in that soft af can only be coated with soft so you can not add a barrier for year two in the areas where the soft wears off.


last year after consulting with a forum member (thanks, it worked) I used international uno (where the soft came off the copper coat didnt really make the grade)

Uno can be applied on to soft.

It is a cross between med/soft and is designed up to 25 knots.

I cruise so rare above 25 and never really use max above a few miles a year and found it was clear of weed and I am told it has nearly worn off, but I have not seen it for myself yet.

I didnt want a build so used uno.

my last boat had a 15 year build up and it starts to crack and flake off, leaving a very rough surface.

International Uno is worth a look.

You could check out the international site and consider one coat of uno .
 
If I lived nearer the boat. I've often thought I'd try some really cheap emulsion paint, liberally dosed with copper powder and uddles of hot chilly sauce.

Surely some one who lives close to their marina, could experiment, with a few pieces of wood/mettal/Fglass. Dunked in the water on pieces of string, with various potions on them.

It cant be that hard.
 
When I bought my current boat, previous owner had applied Seajet. Was told is it quite expensive but it's supposed to hold 3 years before re-applying so saves time and € (or £) each year.

When I took the boat out of the water this winter, there was only some slime at the bottom that came off every easily. Curious how next season holds up ... is there any else that knows or has used this product. Must add though that I'm not based in a (probably more hostile) sea water environment !

Here's a link to manufacturer's website :
SeaJet

Cheers,
Alain
 
We also use Cruiser Uno - one coat and it does the trick for the year. It came out best in a test in MBM a coupleof years ago.
 
I got positive feedbacks from people who tried this system in the med, if you're interested.
Some time ago, I was also tempted to try it on my boat.
I didn't just because of some potential problems with wooden hulls which I wasn't willing to afford.
But it's perfect for grp hulls, afaik. It just requires the removal of all previous A/F paint.
 
i use seajet shogun too and was very tempted this year not to bother reantifouling as last years coat was in good condition and the little slime that was on came off easily
also it doesnt go on thick like others and each year you get a really smooth finish rather than seeing and feeling obvous lines where patches have come off
i dont understand using international uno, its only rated to 25knots..
 
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